The invention relates to a method for manufacturing a base anode having a plurality of adjacently arranged metal elements for a metallurgical vessel, particularly for an electric arc furnace, the intermediate spaces between the metal elements being filled with refractory material and the refractory material being compressed, and a device for implementing this method and a base anode manufactured according to the method.
In electric arc furnaces operated with direct current, the arc current flows from a graphite electrode arranged above the melt through the melt to the base anode; the electric arc furnace thus requires an electrically conducting base. Such bases come in different designs. According to one design (EP-A-0 541 044), the base is provided with metal elements which extend from the surface of the base through the refractory material as far as the metal outer casing of the electric arc furnace. There, the metal elements are fixed to an electrically conducting baseplate which is again fixed to the metal outer casing of the electric arc furnace.
The space between the metal elements, which are preferably designed as sheet steel plates (so-called "fin-type elements") extending vertically upwards from the baseplate, is filled with a refractory lining material, a magnesite lining material for example. The steel plates are arranged in the form of several concentric rings which are often composed of several sectors for base anodes of large diameter.
The intermediate spaces between the steel plates arranged in a ring shape are generally very narrow (less than 100 mm apart) and have a height extending over the entire height--this often exceeds 1 m--of the refractory lining of the base of the electric arc furnace. The problem here is that the refractory lining material can only be inserted into these narrow gaps between the adjacent steel plates with difficulty. Bridge formation and an uneven jointing of the refractory lining material can occur. This causes shrinkage cracks and porous areas through sintering, which leads to a reduced service life for the base anode and the base of the electric arc furnace.
At present the refractory lining material is inserted in layers, the lining material being manually compressed by means of rods or forks each time a layer is inserted. Five to six layers are inserted above each other, until the surface of the base of the arc furnace is reached.
This method is extremely time-consuming and labour-intensive so that the electric arc furnace is shut down for a long time when a base anode needs to be replaced. Furthermore, only a low degree of compression, which is 2.60 kg/dm.sup.3 maximum even in favorable conditions (intermediate spaces which are not too narrow), can be achieved manually.
To avoid the heavy time expenditure according to this method, from pages 199 to 207 of "Radex-Rundschau", No. 4/1992, "Leitende Boden fur Gleichstrom-lichtbogenofen: Bauarten, Zustellung und feuerfeste Baustoffe" (Conducting bases for direct current arc furnaces: designs, lining and refractory materials) it is known to pour in a self-compressing refractory material between the sheet steel plates of the base anode. Although this achieves an even compression within an acceptable lining time, here again compression greater than 2.60 kg/dm.sup.3 cannot be achieved. Both the heat resistance and the resistance to heat erosion leave something to be desired, so that it is still necessary to re-line and/or replace the base anode frequently.
The purpose of the invention is to avoid these disadvantages and difficulties and its object is to create a method for manufacturing a base anode for a metallurgical vessel and a device for implementing the method which enable a high degree of compression of the refractory material inserted in the base anode to be achieved in a relatively short time. In particular, the durability of the base anode should not be substantially below the durability of the lining of the metallurgical vessel surrounding the base anode and the degree of compression of the refractory material inserted into the base anode should be only slightly below the level of the maximum degree of compression for the refractory material that can be achieved in theory.